List of largest stars
=List of largest stars= in the Solar System and several well-known stars: ]] Below is an ordered list of the largest stars currently known by radius. The unit of measurement used is the radius of the Sun (approximately ). The exact order of this list is very incomplete, as great uncertainties currently remain, especially when deriving various important parameters used in calculations, such as stellar luminosity and effective temperature. Often stellar radii can only be expressed as an average or within a large range of values. Values for stellar radii vary significantly in sources and throughout the literature, mostly as the boundary of the very tenuous atmosphere (opacity) greatly differs depending on the wavelength of light in which the star is observed. Radii of several stars can be directly obtained by stellar interferometry. Other methods can use lunar occultations or from eclipsing binaries, which can be used to test other indirect methods of finding true stellar size. Only a few useful supergiant stars can be occulted by the Moon, including Antares and Aldebaran. Examples of eclipsing binaries include Epsilon Aurigae, VV Cephei, and HR 5171. __TOC__ Caveats star VY Canis Majoris compared to the Sun and Earth's orbit.]] Complex issues exist in determining the true radii of the largest stars, which in many cases do display significant errors. The following lists are generally based on various considerations or assumptions that include: * Largest stars are usually expressed in units of the solar radius ( ), where equals 695,700 kilometres. * Stellar radii or diameters are usually only approximated using Stefan–Boltzmann law for the deduced stellar luminosity and effective surface temperature; * Stellar distances, and their errors, for most, remain uncertain or poorly determined; * Many supergiant stars have extended atmospheres and many are embedded within opaque dust shells, making their true effective temperatures highly uncertain; * Many extended supergiant atmospheres also significantly change in size over time, regularly or irregularly pulsating over several months or years as variable stars. This makes adopted luminosities poorly known and may significantly change the quoted radii; * Other direct methods for determining stellar radii, rely on lunar occultations or from eclipses in binary systems. This is only possible for a very small number of stars; * Based on various theoretical evolutionary models, few red supergiants, will exceed 1,500–2,600 times the Sun (roughly 3,000–3,715 K and Mbol = −9 - −9.5 or ). Such limits maybe also depend on the stellar metallicity. Extragalactic large stars In this list are some examples of more distant extragalactic stars, which may have slightly different properties and natures than the currently largest known stars in the Milky Way: * Some red supergiants in the Magellanic Clouds are suspected to have slightly different limiting temperatures and luminosities. Such stars may exceed accepted limits by undergoing large eruptions or change their spectral types over just a few months. * A survey of the Magellanic Clouds has catalogued many red supergiants, where most of them exceed . Largest of these is about 1,200–1,300 . List See also References }} External links * Giant Stars An interactive website comparing the Earth and the Sun to some of the largest known stars * Three largest stars identified BBC News * What is the Biggest Star in the Universe? Universe Today